Electrical connectors

ABSTRACT

According to the invention a wire trap comprising coacting first and second parts carried by respective first and second components of a housing for the trap, which housing defines a wire passage leading to the trap and which components are relatively movable from an open condition of the trap, in which a wire end may be interposed between the separated parts, to a closed condition of the trap, in which the wire end is bent transverse to the wire passage by the first part and is trapped in contact with the second part by the first part, is characterised in that the first part is provided with a slot in the end thereof which is closest to the second part, said slot narrowing in the direction away from said end, whereby a wire end can become wedged in the slot as well as being trapped between the first and second parts.

TECHNICAL FIELD

This invention relates to a wire trap having first and second partswhich coact to trap a wire end therebetween to leave at least one ofsaid parts in secure electrical communication with the wire end.

The invention is expected to find its main application in electricalconnectors (e.g. power plugs, switches and sockets) and in particularconnectors in which closing of the wire trap is occasioned by a relativemovement between two components of the connector, the said movementcausing the wire end to be bent transversely as it enters the closingtrap. A particularly important application is expected to be connectorsin which a turning movement of one component relative to the other (e.g.through substantially a right angle) is used to close the wire traparound the wire end. One example of a connector employing such wiretraps is described in GB-B-2198598 and EP-A-0277800 and in these priorart examples each trap comprises male and female parts, the male partentering into the female part to trap a wire end therebetween.

One problem in connection with the operation of wire traps of the kinddisclosed in the aforesaid patent specifications is the security oftrapping of the wire end in the trap. In some circumstances, smallerdiameter wire ends are less securely trapped than larger diameter wireends. Entrapment which is less secure than a required minimum can leadto resistive heating of the wire trap on current flow and/or the risk ofdislodgement of the wire end from the trap on the appearance of tensionapplied lengthwise of the wire leading to the trap. Both these effectsare undesirable and this invention seeks to obviate these disadvantages.

SUMMARY OF THE INVENTION

According to the invention a wire trap comprising coacting first andsecond parts carried by respective first and second components of ahousing for the trap, which housing defines a wire passage leading tothe trap and which components are relatively movable from an opencondition of the trap, in which a wire end may be interposed between theseparated parts, to a closed condition of the trap, in which the wireend is bent transverse to the wire passage by the first part and istrapped in contact with the second part by the first part, ischaracterised in that the first part is provided with a slot in the endthereof which is closest to the second part, said slot narrowing in thedirection away from said end, whereby a wire end can become wedged inthe slot as well as being trapped between the first and second parts.

The first part can be a blade exhibiting a generally V-shaped slot andthe second part can be a plate-shaped member against which the wire endis pressed by the first member. Conveniently, however, the second partis a generally U-shaped receptor (the plane of the U being normal to theplane of the V) into which the blade enters in the closed condition ofthe trap.

Typically both first and second parts will be of electrically conductingmaterial but this is not necessary provided good electrical contact issecured between the wire end and one of the trap parts.

The shaping of the slot is not seen as being a critical factor andV-shaped slots of semi-angles in the range from under 10° to over 45°have been used successfully. Conveniently the slot has a wide mouth togather stray wires, but a shallow taper at the narrow end to provide aneffective trapping action. In some circumstances (e.g. in a three-pinelectrical plug), dimensional constraints limit the slot depth to some 5mm and this may make a slot with curved edges desirable. One such slotwith curved edges effectively gave a wide taper of semi-angle circa 50°at the mouth and a narrow taper of semi-angle circa 12° at the narrowend. A straight-edged V-shaped slot of semi-angle between 20° and 30°(preferably about 25°) and depth of between 4 and 6 mm measured alongthe line bisecting the angle has proved to be effective with a varietyof stranded wire ends of cross-sectional areas in the range between 0.5mm² and 1.5 mm².

For a pluri-wire connector (e.g. a three-pin electrical plug) a trap canbe provided for each wire and these are conveniently ganged togetherwhereby a relative movement of the component parts of the housing intothe closed condition of the trap snags each wire in the slot of thefirst part of the respective trap, as the first part squeezes the wirebetween the two parts.

BRIEF DESCRIPTION OF DRAWINGS

The invention will now be further described, by way of example withreference to the accompanying drawings, in which:

FIG. 1 is a schematic side view of a male trap part shown with a slot inits leading end and with two wires of different sizes located in theslot,

FIG. 2 is a schematic plan of a closed trap showing the male part in thefemale part, but without a wire present,

FIG. 3 shows the trap of FIG. 2 closed around a thin wire,

FIG. 4 shows the trap of FIG. 2 closed around a thick wire,

FIG. 5 shows a 3-pin electrical plug to which the invention has beenapplied with the plug housing in its open condition, and

FIG. 6 shows a perspective view of the plug of FIG. 5 with its plughousing in the closed condition.

DESCRIPTION OF PREFERRED EMBODIMENTS

FIG. 2 shows a wire trap (generally designated 10) comprising a femalepart 11 partially surrounding a male part 12.

The part 11 can be a cradle of sprung steel strip captive in a firsthousing component 13 and the male part 12 can be a blade of electricallyconducting material (e.g. brass or phosphor bronze) connected to a plugpin 15 mounted in a second housing component 14. The trap 10 is shown inclosed condition in FIG. 2 but without a wire end trapped therein. Apassage through which the wire passes to the trap 10 is shownschematically at 16 in FIG. 2. Where the cradle 11 is required to becurrentcarrying it could be made of phosphor bronze.

FIG. 1 shows the male part 12 and indicates how the leading end 17 ofthe blade is indented with a slot 18, the slot 18 narrowing in thedirection away from the end 17. A thin wire end 19 and a thick wire end20 are schematically shown in cross-section located in the slot in therespective position they naturally adopt when wedged therein.

Because the slot 18 narrows in the direction away from the end 17, asthe trap closes into the condition shown in FIGS. 3 and 4 (e.g. bymoving the blade 12 to the right past the end of the passage 16 and intothe cradle 11, or by moving the cradle 11 to the left relative to theblade 12), the wire end (19 or 20) gets drawn into the slot 18 as far asits diameter will allow and then gets wedged therein when the blade 12is correctly located in the cradle 11. The condition for a thin wire end19 is shown in FIG. 3 and for a thick wire end 20 is shown in FIG. 4. Toaccommodate stranded wires of cross-sectional areas ranging between 0.5mm² and 1.5 mm², the slot 18 can have a depth "d" along the linebisecting the angle of 4.5 mm and a semi-angle θ of 26°.

The dashed line 21 in FIG. 1, which bisects the slot 18, would normallybe aligned with the centre (in the direction normal to the plane of thepaper) of the wire passage 16 and the centre of the cradle 11.

An alternative trap can be constructed in which the cradle 11 isreplaced by a straight receptor (which can be thought of as being thelower limb 11a of the cradle as shown in FIGS. 2 to 4) and this need notbe of electrically conducting material. Generally it is desirable forthere to be at least a length of 0.5 mm between the end of the cradle 11(or its equivalent straight receptor) closest to the wire passage 16 andthe narrow end of the V-slot 18 in the closed condition of the trap(i.e. the distance shown "m" in FIG. 2). Distances for "m" in the range0.5 mm to 2.0 mm would be typical with stranded wires of cross-sectionalareas in the range 0.5 mm² to 1.5 mm². Where a straight receptor is usedit is important to ensure there is some mechanical relationship betweenthe two trap parts so that in the closed condition the two trap partsare kept close enough to lock the wire end therebetween. A gap typicallyof not more than 1 mm (unsprung) will be required for wires of thecross-sectional areas stipulated above.

It is surprising that the U-shaped cradle 11 can be dispensed with andit is felt that this has been made possible by the improvedcurrent-carrying capacity and contact-security that follows from the useof a slot 18 in the blade 12.

FIGS. 5 and 6 show an electrical three-pin plug which incorporates threewire traps (not shown) in accordance with the invention.

FIG. 5 shows a three-core electrical cable 20 with neutral wire 21, anearth wire 22 and a live wire 23 exposed for equal lengths within thehousing 24 of the three-pin plug. Each wire 21-23 has its end 21a, 22a,23a bared and located in a respective wire passage 16 leading to arespective two-part trap 10 of the kind described with reference toFIGS. 1 to 4. After inserting the wire ends 21a-23a fully into therespective passages 16, the central core 14 of the housing 24 is turnedin the direction of the arrow A relative to the outer cap 13 of thehousing, to close all three traps substantially simultaneously and leaveeach pin 21b, 22b, 23b electrically connected to the respective wire end21a, 22a, 23a via a wedging in the respective slot 18 and entrapment ofthe respective blade 12 in the cradle 11. FIG. 6 shows the plug in thiscondition with a fuse carrier 30 occupying the opening 29 in the core 14of the plug and locking the central core 14 in the outer cap 13 in theposition in which all three wire traps are in their closed condition. Acartridge fuse (not shown) in the fuse carrier is now electricallyinterposed between the trap for the live wire 23 and the pin 23btherefor.

I claim:
 1. For an electrical connector having two relatively-movablehousing components displaceable between an open position and a closedposition, and a wire passage in one of said components to receive a wireend with the terminal end of the wire projecting from one end of thepassage,an improved wire trap positioned adjacent the one end of thepassage comprising coacting first and second parts carried by therespective relatively-movable components of said housing, said first andsecond parts being spaced apart on opposite sides of said passage whensaid housing is in the open position and being overlapped when thehousing is in the closed position, the improvement wherein the coactingparts of the wire trap are adapted, when the housing components aredisplaced from open to closed position, to bend a wire extending fromthe passage transverse to the passage and to trap the bent wire betweenthe overlapped parts, said first part being provided with a slot in themouth end thereof which confronts the second part when the housing is inthe open position, said slot narrowing in the direction away from saidmouth end whereby the relatively-movable first and second parts of thewire trap act to wedge the wire end into the slot in the closedposition.
 2. A wire trap according to claim 1, wherein the first part isa blade exhibiting a generally V-shaped slot and the second part is aplate-shaped member against which the wire end is pressed by the firstmember.
 3. A wire trap according to claim 1, wherein the first part is ablade exhibiting a generally V-shaped slot and the second part is agenerally U-shaped receptor having the plane of the U normal to theplane of the V and into which receptor the blade enters in the closedposition of the housing.
 4. A wire trap according to claim 1, whereinthe slot is generally V-shaped and has a semi-angle in the range from10° to 45°.
 5. A wire trap according to claim 1, wherein the slotprovides a taper of a semi-angle of about 50° at a mouth thereof and anarrower taper of a semi-angle of about 12° towards the closed endthereof.
 6. A wire trap according to claim 1, wherein the slot is astraight-edged V-shaped slot of semi-angle between 20° and 30° and adepth of the slot measured along the line bisecting the angle of between4 and 6 mm.
 7. An electrical connector for a plurality of wiresincorporating a plurality of wire traps according to claim 1, one foreach of the plurality of wires, wherein the wire traps are gangedtogether so that upon relative movement of the components of the housingfrom the open position into the closed position, a trap snags each wirein the slot of the first part of the respective trap, as the closing ofthe components squeezes the wire between the two parts.
 8. A connectoraccording to claim 7, wherein the components are mounted for relativerotary movement about a turning axis, and the relative movement of thecomponents of the housing closes and opens the wire trap partscircumferentially of said turning axis.
 9. A three-trap connectoraccording to claim 8 in which the housing is in the form of a three-pinelectrical plug, the housing components comprising a central coreturnable within an outer cap, pins projecting from one side of thecentral core, and a wire-receiving opening in the central core, each pinbeing in electrical contact with one part of a respective wire trap, thewire passage of each of said plurality of wire traps being in saidcentral core and leading from said wire-receiving opening to therespective one of the three wire traps.
 10. A connector according toclaim 9 including a fuse carrier adapted to engage in the wire-receivingopening of the central core and having a part adapted to engage theouter cap and prevent relative turning of the core in the outer cap andthus a reopening of the wire traps.
 11. For an electrical connectorhaving two relatively-movable housing components displaceable between anopen position and a closed position, and a wire passage in one of saidcomponents to receive a wire end with the terminal end of the wireprojecting from one end of the passage,an improved wire trap positionedadjacent the one end of the passage comprising coacting first and secondparts carried by the respective relatively-movable components of saidhousing, said first and second parts being spaced apart on oppositesides of said passage when said housing is in the open position andbeing overlapped when the housing is in the closed position, theimprovement wherein the coacting parts of the wire trap are adapted,when the housing components are displaced from open to closed position,to bend a wire extending from the passage transverse to the passage andto trap the bent wire between the overlapped parts, said first partbeing provided with a slot in the mouth end thereof which confronts thesecond part when the housing is in the open position, said slotnarrowing in the direction away from said mouth end whereby thedisplacement of the relatively-movable components of the housing fromthe open position to the closed position concomitantly bends the wireend transverse to said wire passage to lie between the first and secondtrap parts, bends the wire end transversely again to lie in saidnarrowing slot in said first trap part, and wedges the wire in saidnarrowing slot as the trap closes.
 12. For an electrical connectorhaving two relatively-movable housing components displaceable between anopen position and a closed position, and a wire passage in one of saidcomponents to receive a wire end with the terminal end of the wireprojecting from one end of the passage,an improved wire trap positionedadjacent the one end of the passage comprising a first blade partcoacting with a second U-shaped receptor part carried by the respectiverelatively-movable components of said housing, said first and secondparts being spaced apart on opposite sides of said passage when saidhousing is in the open position and the blade part inserted within theU-shaped part when the housing is in the closed position, theimprovement wherein the coacting parts of the wire trap are adapted,when the housing components are displaced from open to closed position,to bend a wire extending from the passage transverse to the passage andto bend the end of the wire into a U-shaped to trap the bent wirebetween the inserted parts, said first part being provided with a slotin the mouth end thereof which confronts the second part when thehousing is in the open position, said slot narrowing in the directionaway from said mouth end whereby the relatively-movable first and secondparts of the wire trap act to wedge the U-shaped wire end into the slotin the closed position.